com.graphhopper.routing.subnetwork

Class TarjanSCC

java.lang.Object

com.graphhopper.routing.subnetwork.TarjanSCC

public class TarjanSCC
extends Object

Tarjan's algorithm to find strongly connected components of a directed graph. Two nodes belong to the same connected component iff they are reachable from each other. Reachability from A to B is not necessarily equal to reachability from B to A because the graph is directed.

This class offers two ways to run the algorithm: Either using (function call) recursion findComponentsRecursive() or recursion using an explicit stack findComponents(). The first one is easier to implement and understand and the second one allows running the algorithm also on large graphs without having to deal with JVM stack size limits.

Tarjan's algorithm is explained for example here: - http://en.wikipedia.org/wiki/Tarjan's_strongly_connected_components_algorithm - http://www.timl.id.au/?p=327 - http://homepages.ecs.vuw.ac.nz/~djp/files/P05.pdf

Author:

easbar

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	TarjanSCC.ConnectedComponents

Constructor Summary

Constructors

Constructor and Description
TarjanSCC(Graph graph, BooleanEncodedValue accessEnc, boolean excludeSingleNodeComponents)

Method Summary

Modifier and Type	Method and Description
TarjanSCC.ConnectedComponents	findComponents() Runs Tarjan's algorithm using an explicit stack.
TarjanSCC.ConnectedComponents	findComponentsRecursive() Runs Tarjan's algorithm in a recursive way.
void	setAdditionalEdgeFilter(EdgeFilter additionalFilter) Allows adding an additional edge filter to exclude edges while searching for connected components.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TarjanSCC

public TarjanSCC(Graph graph,
                 BooleanEncodedValue accessEnc,
                 boolean excludeSingleNodeComponents)

Parameters:

excludeSingleNodeComponents - if set to false components that only contain a single node will not be returned when calling findComponents() or findComponentsRecursive(), which can be useful to save some memory.

Method Detail

setAdditionalEdgeFilter

public void setAdditionalEdgeFilter(EdgeFilter additionalFilter)

Allows adding an additional edge filter to exclude edges while searching for connected components.

findComponentsRecursive

public TarjanSCC.ConnectedComponents findComponentsRecursive()

Runs Tarjan's algorithm in a recursive way. Doing it like this requires a large stack size for large graphs, which can be set like `-Xss1024M`. Usually the version using an explicit stack (findComponents()) should be preferred. However, this recursive implementation is easier to understand.

findComponents

public TarjanSCC.ConnectedComponents findComponents()

Runs Tarjan's algorithm using an explicit stack.